The purpose of this project is definition of structural differences and similarities of selected surface-exposed constituents of gonococci from various strains and intrastrain variants. During the current year, results have yielded a modified model for disposition of outer membrane protein I; protein I constituents from organisms causing disseminated gonococcal infections were found to expose only one end of their subunits to the external environment. This contrasts with the protein I subunits of organisms causing local gonorrheal infections inasmuch as these forms of protein I seem to have a "hairpin" orientation in the outer membrane with a mid-portion of these molecules being exposed on the organisms' surfaces. The major effort on this project during the past year has been definition of the structural variations in pilus subunits that can be delineated among variants of individual gonococcal strains. It was found that at least a dozen different subunit forms (by size) of pili occur among these intrastrain variants. These findings predict that formulation of a pilus-based vaccine for gonorrhea will have to include many more serotypes of pili than was previously appreciated. Genetic mechanisms responsible for both pilus expression and for variation in pilus subunit form are being investigated.